Low-crosstalk large-capacity few-mode optical fiber

Abstract

A low-crosstalk large-capacity few-mode optical fiber includes an optical fiber cladding. Few-mode units are arranged in the optical fiber cladding, each few-mode unit sequentially includes a few-mode fiber core, an inner cladding and a trench from inside to outside, and a high-refractive-index ring is arranged in the few-mode fiber core. The few-mode units include first few-mode subunits, second few-mode subunits and third few-mode subunits, where the first few-mode subunits, the second few-mode subunits and the third few-mode subunits are arranged at intervals. The first few-mode subunit includes a first few-mode fiber core, the second few-mode subunit includes a second few-mode fiber core, and the third few-mode subunit includes a third few-mode fiber core, the radii and refractive indexes of the first few-mode fiber cores, the second few-mode fiber cores and the third few-mode fiber cores being different, respectively.

What is claimed is: 
     
       1. A low-crosstalk large-capacity few-mode optical fiber, comprising an optical fiber cladding, wherein few-mode units are arranged in the optical fiber cladding, each of the few-mode units sequentially comprises a few-mode fiber core, an inner cladding and a trench from inside to outside, and a high-refractive-index ring is arranged in the few-mode fiber core; the few-mode units comprise first few-mode subunits, second few-mode subunits and third few-mode subunits, wherein the first few-mode subunits, the second few-mode subunits and the third few-mode subunits are arranged at intervals; and
 each of the first few-mode subunits comprises a first few-mode fiber core, each of the second few-mode subunits comprises a second few-mode fiber core, and each of the third few-mode subunits comprises a third few-mode fiber core, wherein radii of the first few-mode fiber cores, the second few-mode fiber cores and the third few-mode fiber cores are different, and refractive indexes of the first few-mode fiber cores, the second few-mode fiber cores and the third few-mode fiber cores are different; 
 wherein the optical fiber cladding is made of a silica material, the inner cladding is made of a silica material, the trench is made of a silica material doped with fluorine, the few-mode fiber core is made of a silica material doped with germanium dioxide, and the high-refractive-index ring is made of a silica material doped with high-concentration germanium dioxide; 
 wherein the few-mode units have a step-type distribution design in refractive indexes; 
 wherein the optical fiber cladding has a refractive index of n 0 , the inner cladding has a refractive index of n 0 , the trench has a refractive index of n 3 , the first few-mode fiber core has a refractive index of n 1 , the second few-mode fiber core has a refractive index of n 4 , and the third few-mode fiber core has a refractive index of n 6 ; 
 each of the first few-mode subunits comprises a first high-refractive-index ring, each of the second few-mode subunits comprises a second high-refractive-index ring, and each of the third few-mode subunits comprises a third high-refractive-index ring, wherein the first high-refractive-index ring has a refractive index of n 2 , the second high-refractive-index ring has a refractive index of n 5 , and the third high-refractive-index ring has a refractive index of n 7  and 
 the n 1  is greater than the n 0 , the n 2  is greater than the n 1 , the n 3  is less than the n 0 , the n 4  is greater than the n 0 , the n 5  is greater than the n 4 , the n 6  is greater than the n 0 , and the n 7  is greater than the n 6 . 
 
     
     
       2. The low-crosstalk large-capacity few-mode optical fiber according to  claim 1 , wherein the first few-mode fiber core, the second few-mode fiber core and the third few-mode fiber core are configured to transmit an LP 01  mode , an LP 11  mode, an LP 21  mode and an LP 02  mode. 
     
     
       3. The low-crosstalk large-capacity few-mode optical fiber according to  claim 1 , wherein (n 1 −n 0 )/n 1  is kept within 0.92%, (n 2 −n 1 )/n 2  is kept within 0.25%, and (n 0 −n 3 )/n 0  is controlled within 0.7%; (n 4 −n 0 )/n 4  is kept within 0.96%, (n 5   31  n 4 )n 5  is kept within 0.25%, and (n 0 −n 3 )/n 0  is controlled within 0.7%; (n 6 −n 0 )/n 6  is kept within 0.88%, (n 7 −n 0 )/n 7  is kept within 0.25%, and (n 0 −n 3 )/n 0  is controlled within 0.7%. 
     
     
       4. The low-crosstalk large-capacity few-mode optical fiber according to claim I, wherein the low-crosstalk large-capacity few-mode optical fiber is a heterogeneous thirteen-core few-mode optical fiber. 
     
     
       5. A low-crosstalk large-capacity few-mode optical fiber, comprising an optical fiber cladding, wherein few-mode units are arranged in the optical fiber cladding, each of the few-mode units sequentially comprises a few-mode fiber core, an inner cladding and a trench from inside to outside, and a high-refracture-index ring is arranged in the few-mode fiber core; the few-mode units comprise first few-mode subunits, second few-mode subunits and third few-mode subunits, wherein the first few-mode subunits, the second few-mode subunits and the third few-mode subunits are arranged at intervals; and
 each of the first few-mode subunits comprises a first few-mode fiber core, each of the second few-mode subunits comprises a second few-mode fiber core, and each of the third few-mode subunits comprises a third few-mode fiber core. wherein radii of the first few-mode fiber cores, the second few-mode fiber cores and the third few-mode fiber cores are different, and refractive indexes of the first few-mode fiber cores, the second few-mode fiber cores and the third few-mode fiber cores are different; 
 wherein the low-crosstalk large-capacity few-mode optical fiber is a heterogeneous thirteen-core few-mode optical fiber: and 
 wherein one of the first few-mode subunits is arranged at a center of the low-crosstalk large-capacity few-mode optical fiber, three of the second few-mode subunits and three of the third few-mode subunits are arranged at intervals around the center of the low-crosstalk large-capacity few-mode optical fiber, connecting lines of geometric centers of the second few-mode subunits and the third few-mode subunits form a first-layer regular hexagon with a core pitch as a side length, and six of the first few-mode subunits are located on connecting lines of midpoints of three pairs of opposite sides of the first-layer regular hexagon and are at a distance of √{square root over (3)}-fold core pitch away from the center of the low-crosstalk large-capacity few-mode optical fiber. 
 
     
     
       6. The low-crosstalk large-capacity few-mode optical fiber according to  claim 5 , wherein a second few-mode subunit of the second few-mode subunits and a third few-mode subunit of the third few-mode subunits are adjacent to each other on the first-layer regular hexagon, and the second few-mode subunit and the third few-mode subunit form a first equilateral triangle with the first few-mode subunit at the center of the low-crosstalk large-capacity few-mode optical fiber, and form a second equilateral triangle with the corresponding first few-mode subunit at an outermost layer; and the first few-mode subunit at the outermost layer is arranged on a perpendicular bisector of the side length formed by connecting the second few-mode subunit and the third few-mode subunit. 
     
     
       7. The low-crosstalk large-capacity few-mode optical fiber according to  claim 6 , wherein a first effective refractive index difference between an LP 21  mode and an LP 02  mode transmitted in the first few-mode fiber core is 2×10 −3 , a second effective refractive index difference between the LP 21  mode and the LP 02  mode transmitted in the second few-mode fiber is 2×1 −3 , and a third effective refractive index difference between the LP 21  mode and the LP 02  mode transmitted in the third few-mode fiber is 2×10 −3 .